Energy savings through late-steam injection - A new technique for improving wood pellet production

Wood pellet production has developed into an important global industry. Improving pre-processing operations is vital in keeping the industry competitive as energy and material inputs are reflected in the cost and sustainability of wood pellets as a product. In this study, a new method of steam conditioning in pelleting was evaluated based on semi-industrial experiments and thermodynamics principles. Late-steam injection was compared to conventional steam conditioning in an industrial production scenario of 100,000 tonnes per year using a rotating ring-die pellet mill, the most common mill type used in the industry. The differences in energy use and production cost were determined and the environmental footprint of produced pellets was assessed using the renewable energy directive (RED) framework for biofuels. The results showed that late-steam injection dramatically reduced steam consumption and feedstock drying needs in pelleting and, to a lesser extent, the mill-specific energy use. The economic benefit, based on the industrial production scenario, equated to an annual operational savings of 0.25 MV (3.9 %) which, over a ten-year plant lifetime, had a present value of 1.3 MV. The CO2-equivalent emissions of produced pellets, for co-firing applications, was significantly improved. These findings were specific to rotating ring-die pellet mills so that the potential for retrofitting late-steam injection solutions in existing industrial sites is large. The technology is seen as a means of increasing the competitiveness of global wood pellet production. (C) 2020 Elsevier Ltd. All rights reserved.